1. Field
This disclosure relates to signal coincidence detection circuits.
2. Description of Related Art
In analog circuits it is often desirable to determine when two signals are coincident. For purposes of this disclosure, coincidence (or signal coincidence) means that two (or more) voltage signals have substantially the same voltage amplitude at substantially the same point in time. For instance, such (signal) coincidence may be established when the signals being compared are all within a certain range relative to each other (e.g., within a certain percentage or within a certain difference in amplitude). For instance, in a particular embodiment, two signals may be considered to be coincident if they have voltage amplitudes that are within 100 mV of each other. The 100 mV difference may be termed a “coincidence band” or “band of coincidence.” In such an embodiment, a voltage signal of 2.9 V would be considered to be coincident with a voltage signal of 2.95 V, while the signal of 2.9 V would not be considered coincident with a voltage signal of 2.85 V. As is known, such signal coincidence may be determined using a signal coincidence detection circuit.
An example application for such signal coincidence detection circuits is their use to determine “lock” of bandgap reference circuits. Bandgap reference circuits are known and will not be described in detail here. Briefly, however, bandgap reference circuits are used to provide stable voltage references in low-voltage circuits (e.g., ˜1.2 V). Additionally, bandgap reference circuits may be used to provide local biases in very large scale integrated circuits. Local biases generated by such bandgap circuits are desirable because they are not substantially affected by ambient noise or transient signals. Bandgap circuits are feedback circuits where a reference signal is applied and a feedback signal is generated based on the reference signal. The bandgap circuit is considered to be “locked” when the feedback signal is coincident (e.g., within a band of coincidence) with the reference signal. As indicated above, such coincidence may be determined using a signal coincidence detection circuit. However, current approaches for implementing such signal coincidence detection circuits have certain drawbacks.
For instance, current embodiments of signal coincidence detection circuits are fairly complicated analog circuits (e.g., including fifty or more transistors). Such circuits include a series of comparators, where shifts in the threshold of the comparators are used to establish a coincidence band for the signals being compared by the circuit. Such signal coincidence detection circuits also include logic circuitry that is used to determine coincidence between signals of interest (e.g., a reference signal and a feedback signal of a bandgap reference circuit) based on signals that are generated by the series of comparators from the signals of interest. However, because of their complexity, such signal coincidence detection circuits have relatively high power dissipation, may operate slowly and are difficult to design.
Furthermore, it may be desirable to establish a threshold voltage for coincidence detection (e.g., a voltage level below which coincidence of signals being compared will not be indicated) so that coincidence of the signals being compared that occurs below the threshold voltage is not indicated. In such an approach, additional circuitry is needed for setting such a threshold. Such threshold circuitry thus further increases the design complexity and power dissipation of such circuits. Based on the foregoing, alternative approaches for implementing such signal detection circuits are desirable.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.